Data compression is the reduction or elimination of redundancy in data representation in order to achieve savings in storage and communication costs. Data compression techniques can be broadly classified into two categories: lossless and lossy techniques. In lossless techniques, the exact original data can be recovered while in lossy techniques a close approximation of the original data can be obtained. The lossless methods are also called entropy coding techniques since there is no loss of information content during the process of compression. Lossless techniques are used for text compression and image compression in certain environments such as medical imaging where no loss of information is tolerated and typically the compression ratio is around 3:1. Lossy compression techniques are commonly applied in image and audio compression and depending upon the fidelity required much higher compression ratios can be obtained.
Digital images require an enormous amount of space for storage. For example, a color image with a resolution of 1024.times.1024 picture elements (pixels) with 24 bits per pixel would require 3.15M bytes in uncompressed form. At a video rate of 30 frames per second, this requires a data rate of 94M bytes per second. With the recent advances in video applications such as video teleconferencing, HDTV, home entertainment systems, interactive visualization and multimedia, there is an increasing demand for even higher bandwidth computing and communication systems. Very high speed implementation of efficient image compression techniques will significantly help in meeting that challenge.
In recent years, a working group known as Joint Photographic Expert Group (JPEG) consisting of three international standard organizations, International Telegraph and Telephone Consultative Committee (CCITT), International Organization for Standardization (ISO) and International Electrotechnical Commission (IEC), has defined an international standard for coding and compression of continuous-tone still images. This standard is commonly referred to as the JPEG standard. The primary aim of the JPEG standard is to propose an image compression technique that would be application independent and aid VLSI implementation of data compression.